[docker] How do I edit a file after I shell to a Docker container?

I successfully shelled to a Docker container using:

docker exec -i -t 69f1711a205e bash

Now I need to edit file and I don't have any editors inside:

root@69f1711a205e:/# nano
bash: nano: command not found
root@69f1711a205e:/# pico
bash: pico: command not found
root@69f1711a205e:/# vi
bash: vi: command not found
root@69f1711a205e:/# vim
bash: vim: command not found
root@69f1711a205e:/# emacs
bash: emacs: command not found
root@69f1711a205e:/#

How do I edit files?

You can open existing file with

cat filename.extension

and copy all the existing text on clipboard.

Then delete old file with

rm filename.extension

or rename old file with

mv old-filename.extension new-filename.extension

Create new file with

cat > new-file.extension

Then paste all text copied on clipboard, press Enter and exit with save by pressing ctrl+z. And voila no need to install any kind of editors.

For common edit operations I prefer to install vi (vim-tiny), which uses only 1491 kB or nano which uses 1707 kB.

In other hand vim uses 28.9 MB.

We have to remember that in order for apt-get install to work, we have to do the update the first time, so:

apt-get update
apt-get install vim-tiny

To start the editor in CLI we need to enter vi.

You can also use a special container which will contain only the command you need: Vim. I chose python-vim. It assumes that the data you want to edit are in a data container built with the following Dockerfile:

FROM debian:jessie
ENV MY_USER_PASS my_user_pass
RUN groupadd --gid 1001 my_user
RUN useradd -ms /bin/bash --home /home/my_user \
            -p $(echo "print crypt("${MY_USER_PASS:-password}", "salt")" | perl) \
            --uid 1001 --gid 1001 my_user
ADD src /home/my_user/src
RUN chown -R my_user:my_user /home/my_user/src
RUN chmod u+x /home/my_user/src
CMD ["true"]

You will be able to edit your data by mounting a Docker volume (src_volume) which will be shared by your data container (src_data) and the python-vim container.

docker volume create --name src_volume
docker build -t src_data .
docker run -d -v src_volume:/home/my_user/src --name src_data_1 src_data
docker run --rm -it -v src_volume:/src fedeg/python-vim:latest

That way, you do not change your containers. You just use a special container for this work.

If you use Windows container and you want change any file, you can get and use Vim in Powershell console easily.

To shelled to the Windows Docker container with PowerShell:

docker exec -it <name> powershell

• First install Chocolatey package manager

  Invoke-WebRequest https://chocolatey.org/install.ps1 -UseBasicParsing | Invoke-Expression;

• Install Vim

  choco install vim

• Refresh ENVIRONMENTAL VARIABLE You can just exit and shell back to the container

• Go to file location and Vim it vim file.txt

After you shelled to the Docker container, just type:

apt-get update
apt-get install nano

See Stack Overflow question sed edit file in place

It would be a good option here, if:

1. To modify a large file, it's impossible to use cat.

2. Install Vim is not allowed or takes too long. My situation is using the MySQL 5.7 image when I want to change the my.cnf file, there is no vim, vi, and Vim install takes too long (China Great Firewall). sed is provided in the image, and it's quite simple. My usage is like

   sed -i /s/testtobechanged/textwanted/g filename

   Use man sed or look for other tutorials for more complex usage.

If you don't want to add an editor just to make a few small changes (e.g., change the Tomcat configuration), you can just use:

docker cp <container>:/path/to/file.ext .

which copies it to your local machine (to your current directory). Then edit the file locally using your favorite editor, and then do a

docker cp file.ext <container>:/path/to/file.ext

to replace the old file.

To keep your Docker images small, don't install unnecessary editors. You can edit the files over SSH from the Docker host to the container:

vim scp://remoteuser@containerip//path/to/document

You can use cat if installed, with the > caracter. Here is the manipulation :

cat > file_to_edit
#1 Write or Paste you text
#2 don't forget to leave a blank line at the end of file
#3 Ctrl + C to apply configuration

Now you can see the result with the command

cat file

You can use cat if it's installed, which will most likely be the case if it's not a bare/raw container. It works in a pinch, and ok when copy+pasting to a proper editor locally.

cat > file
# 1. type in your content
# 2. leave a newline at end of file
# 3. ctrl-c / (better: ctrl-d)
cat file

cat will output each line on receiving a newline. Make sure to add a newline for that last line. ctrl-c sends a SIGINT for cat to exit gracefully. From the comments you see that you can also hit ctrl-d to denote end-of-file ("no more input coming").

Another option is something like infilter which injects a process into the container namespace with some ptrace magic: https://github.com/yadutaf/infilter

You can just edit your file on host and quickly copy it into and run it inside the container. Here is my one-line shortcut to copy and run a Python file:

docker cp main.py my-container:/data/scripts/ ; docker exec -it my-container python /data/scripts/main.py

An easy way to edit a few lines would be:

echo "deb http://deb.debian.org/debian stretch main" > sources.list

I use "docker run" (not "docker exec"), and I'm in a restricted zone where we cannot install an editor. But I have an editor on the Docker host.

My workaround is: Bind mount a volume from the Docker host to the container (https://docs.docker.com/engine/reference/run/#/volume-shared-filesystems), and edit the file outside the container. It looks like this:

docker run -v /outside/dir:/container/dir

This is mostly for experimenting, and later I'd change the file when building the image.

Sometime you must first run the container with root:

docker exec -ti --user root <container-id> /bin/bash

Then in the container, to install Vim or something else:

apt-get install vim

It is kind of screwy, but in a pinch you can use sed or awk to make small edits or remove text. Be careful with your regex targets of course and be aware that you're likely root on your container and might have to re-adjust permissions.

For example, removing a full line that contains text matching a regex:

awk '!/targetText/' file.txt > temp && mv temp file.txt

(More)